This invention relates to apparatus for compression crimping fibrous material. More particularly, this invention relates to improvements involving control of the apparatus in response to the position in the crimping zone of the apparatus of the plug of crimped fibrous material which is formed in the crimping zone.
Various apparatus for compression crimping fibrous material are known which comprise means defining a compression crimping zone, means for feeding fibrous material into the compression crimping zone and at least one movable member defining a lateral wall of the zone and being biased toward the fibrous material to restrict egress of the fibrous material from the zone and thereby exert a back pressure on the fibrous material, causing the fibrous material to buckle and thereby crimp in the zone. More particularly, the movable member may be a pressure shoe. A pair of such shoes, which are arranged opposite each other and are biased toward each other, may be employed. The apparatus must be controlled so that the plug itself remains in the crimping zone and the crimped fibrous material is withdrawn from the plug while the plug remains in the crimping zone.
To this end, the apparatus frequently includes means for sensing advance of the plug to a predetermined position in the crimping zone which position represents the forwardmost point that the leading end of the plug is to be permitted to reach. When the leading end of the plug is sensed at this position, means are actuated for increasing the rate of withdrawal of crimped fibrous material from the zone and/or decreasing the rate of feeding of fibrous material to the zone. This is continued until the leading end of the plug has withdrawn from said predetermined position. It is readily understood that this requires that the apparatus be operated with a slight overfeed tendency since no sensing device is provided to detect displacement of the leading end in the direction counter to the net direction of travel of the yarn through the crimping zone. Alternatively, a second sensing device at a position in the crimping zone spaced upstream from the first sensing device may be provided, the first sensing device operating as described above and impingement of the leading end of the plug upon the second sensing device causing a decrease in the rate of withdrawal of the yarn from the zone and/or increase in the rate of feed of yarn to the zone and this decrease or increase not being interrupted until the leading end of the plug retreats to a point immediately downstream from the second sensing device. In this case, the apparatus is operated with neither an underfeed nor an overfeed tendency. Yet another alternative, this necessitating operation with a slight underfeed tendency, is to arrange a single sensing device for actuating an increase in the rate of feed of the yarn to the zone and/or a decrease in the rate of withdrawal of the yarn from the zone only when the leading end of the plug retreats so that it is downsteam of the sensing device. In all of these cases, the position of the leading end of the plug is being maintained substantially constant or substantially within a relatively small range so that the yarn is being subjected to substantially constant compression crimping conditions thereby to obtain a substantially uniform product.
Apart from mechanical feelers, which have the disadvantage of contacting the plug and, consequently, perhaps affecting the crimping, a source of visible light and a photoelectric cell have been used as a sensing device for the plug. However, these devices are somewhat non-uniform in their response to the leading end of the plug because they use visible light. For example, the leading end of the plug may have to impinge upon the light directed at the photoelectric cell to different extents depending upon the color of the yarn to cause the same response by the photoelectric cell.
Another problem in the prior art is that a sensing device for the plug, whether mechanically or photoelectrically actuated, may wear out or fail. If no auxiliary sensing device is provided, the plug may then be displaced out of the crimping zone, resulting in lack of adequate control of the crimping and possible fouling of the equipment outside the crimping zone.
It is an object of the invention to provide improved means for sensing the plug, which improved means are free of the aforementioned disadvantages.
It is a further object of the present invention to provide a device to shut down equipment in the event of failure of the plug sensing device, particularly for a compression crimping apparatus employing at least one movable member defining a lateral wall of the compression crimping zone.
Other objects and advantages of the invention will be apparent to one skilled in the art from the following description of the invention.